Windows Server 2012 R2 allows Edition conversion using DISM and the conversion to higher edition is not reversible. If you use Windows Server 2012 R2 Evaluation, you can convert to full version (VL or Retail or OEM).

Now the question is

Can we convert Windows Server 2012 R2 Edition with AD Role from Evaluation to Full Version?

If you try to convert Windows Server 2012 Edition with AD Role Installed from Evaluation to Full Version, DISM command will raise Error 50: Changing this windows edition is not supported online for a domain controller.

To Check Windows Current Edition (Windows Edition should show ServerDatacenter)

DISM /Online /Get-CurrentEdition

To get Domain Info Detail

Get-ADDomain

Conclusions

Windows Server 2012 R2 Edition with Active Directory Role installed can be converted from Evaluation to Full Version. However, Microsoft does not mention this is supported and I advise System Administrator to check with Microsoft before attempting to use this approach in Production.